Relatively rotatable cryogenic transfer system

ABSTRACT

A relatively rotatable cryogenic transfer apparatus for transferring fluid between two relatively rotatable devices which are rotatable relative to each other at significant speeds; said apparatus including a housing, a first unit fixed to the housing and including a first relatively long, stiff, thin, low thermal conductivity conduit; a second unit including a second relatively long, stiff, thin, low thermal conductivity conduit surrounding and spaced from the first unit to provide a first relatively long, narrow relative motion gap that provides a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; first means for relatively rotatably interconnecting the housing and the second unit for maintaining the housing and second unit in uniform spaced alignment and having its heat producing relative motion parts disposed in a first ambient temperature portion of the apparatus proximate the area where the first unit is fixed to the housing remote from the supercooled portions of the apparatus; second means for relatively rotatably interconnecting the housing and the second unit disposed in a second ambient temperature portion of the apparatus spaced from the first ambient temperature portion and remote from the cooler portions of the apparatus; first port means in the housing between the first and second ambient temperature portions; the second unit including a third relatively long, stiff, thin, low thermal conductivity conduit surrounding the second conduit, the third conduit being spaced from the housing to provide a second relatively long, narrow relative motion gap extending from the first port means to the first ambient temperature portion and a third relatively long, narrow relative motion gap extending from the first port means to the second ambient temperature portion; each of the second and third relative motion gaps provide a relatively stagnant environment in which convection currents are minimized and vapor from the fluid acts as an insulator; the first sealing means between the housing and the second unit in the first ambient temperature portion sealing the ambient temperature end of the first relative motion gap and of the second relative motion gap; and second sealing means between the housing and the second unit and the second ambient temperature portion for sealing the ambient temperature end of the third relative motion gap.

United States Patent 1191 Smith, Jr. et al.

[451 Nov. 5, 1974 1 RELATIVELY ROTATABLE CRYOGENIC TRANSFER SYSTEM [75]Inventors: Joseph L. Smith, Jr., Concord;

' Philip Thullen, Dover, both of Mass.

[73] Assignee: Massachusetts Institute of Technology, Cambridge, Mass.

[22] Filed: May 30, 1972 [21] Appl. No.: 257,640

[52] U.S. Cl 62/505, 62/55, 310/54,

310/61 [51] Int. Cl. F25!) 31/12 [58] Field of Search 62/55, 505;310/54, 61

[56] References Cited UNITED STATES PATENTS 12/1971 Lorch 62/505 PrimaryExaminerMeyer Perlin Assistant Examiner--Ronald C. Capossela Attorney,Agent, or Firm-Arthur A. Smith, Jr.; Joseph S. landiorio; Robert Shaw [57 ABSTRACT currents are minimized and vapor from the fluid acts as aninsulator; first means for relatively rotatably interconnecting thehousing and the second unit for maintaining the housing and second unitin uniform spaced alignment and having its heat producing relativemotion parts disposed in a first ambient temperature portion of theapparatus proximate the area where the first unit is fixed to thehousing remote from the supercooled portions of the apparatus; secondmeans for relatively rotatably interconnecting the housing and thesecond unit disposed in a second ambient temperature portion of theapparatus spaced from the first ambient temperature portion and remotefrom the cooler portions of the apparatus; first port means in thehousing between the first and second ambient temperature portions; thesecond unit including a third relatively long, stiff, thin, low thermalconductivity conduit surrounding the second conduit, the third conduitbeing spaced from the housing to provide a second relatively long,narrow relative motion gap extending from the first port means to thefirst ambient temperature portion and a third relatively long, narrowrelative motion gap extending from the first port means to the secondambient temperature portion; each of the second and third relativemotion gaps provide a relatively stagnant environment in whichconvection currents are minimized and vapor from the fluid acts as aninsulator; the first sealing means between the housing and the secondunit in the first ambient temperature portion sealing the ambienttemperature end of the first relative motion gap and of the secondrelative motion gap; and second sealing means between the housing andthe second unit and the second ambient temperature portion for sealingthe ambient temperature end of the third relative motion gap.

4 Claims, 4 Drawing Figures PAIENTEmv sum sum 1 4 3.845.639

l RELATIVELY ROTATABLE CRYOGENIC TRANSFER SYSTEM FIELD OF INVENTION Thisinvention relates to an apparatus for transferring cryogenic fluidbetween a source of the fluid and a device which uses the fluid, andmore particularly such a transfer apparatus wherein the source anddevice are rotatable relative to each other at a significant speed.

BACKGROUND or INVENTION Recently the development of a superconductingalternator was undertaken. In the course of this development it wasdetermined that it was desirable to include in the rotor thesuperconducting winding which produced the magnetic field. It thereforebecame necessary to supply the supercooled fluid, typically liquidHelium, to a rotary vessel. Previously, the cryogenic systems were usedin stationary environments i.e. the part of the system supplying thecoolant and the part to be cooled were not normally rotating or movingrelative to each other during operation. In initial attempts to cool thegenerator rotor, the rotor was immersed in an open top Dewar vesselwhich was rotated about its central vertical axis but the resultingcooling was extremely inefficient and the heating up of the fluid wasmore pronounced than expected. This more pronounced effect wasdiscovered to be due to the centrifugal convection currents which drewwarm, ambient temperature helium gas down about the stationary pipewhich fed the fluid to the Dewar and forced the cooled helium gasagainst the outer wall of the Dewar and up and over the top of thatwall. One attempt to stifle the convection current resulted in a coverbeing placed in the Dewar at the surface of the liquid but the requiredmechanical interconnections of the cover produced frictional heat fromthe contact of the parts which seriously detracted from the coolingefficiency of the system. A further attempt which placed the cover asubstantial distance above the surface was similarly unsuccessfulbecause the closed-loop centrifugal convection currents which occurredin the enclosed space also seriously reduced the efficiency of thesystem. More detailed discussion of these considerations is contained ina thesis, a copy of which is enclosed for deposit in the Patent OfficeLibrary, by W. David Lee, entitled Con- Iinuous Transfer of LiquidHelium to a Rotating Dewar,

submitted in partial fulfillment of the requirements for the degrees ofBachelor of Science and Master of Science, Mechanical EngineeringDepartment, Massachusetts Institute of Technology in June, 1970 anddeposited in the Institutes library Sept. 10, 1970.

SUMMARY OF INVENTION It is therefore an object of this invention toprovide a relatively rotatable transfer system for transferringsupercooled fluid between a stationary member and rotating member.

It is a further object of this invention to provide such a transfersystem inwhich the seals are located in an area of the system remotefrom the supercooled fluid. 7

It is a further object of this invention to provide such a transfersystem in which the coolant stream is protected by an insulation medium.

It is a further object of this invention to provide such a transfersystem in which destructive mechanical vibration and mechanical rubbingbetween parts in the supercooled area are eliminated.

It is a further object of this invention to provide such a transfersystem which is capable of recovering the spent coolant and oftransferring the fluid in and out in separate streams at differenttemperatures.

This invention results from the discovery that despite the many physicallimitations on a relatively, rotatable cryogenic transfer system anefficient, even an extremely efficient system, can be constructed byutilizing a long narrow relative motion gap between the rotating partswhich suppresses centrifugal convection and permits a relativelystagnant column of vapor to reside there as an insulator. The use of along narrow relative motion'gap also reduces the convection of heat tothe supercooled region by the small centrifugal convection flow; coldgas moves toward the warm region near the outer wall of the relativemotion gap and warm gas moves toward the cold end near the inner wall ofthe relative motion gap. As the gap becomes small these two countercurrents come close together and heat may flow readily from the warm tothe cold current. Thus the warm gas is precooled by the cold gas beforethe warm gas reaches the supercooled region thus further reducing theenergy carried into the supercooled region. The long length of the gapfurther enables the necessary contacting parts, producers of frictionalheat, to be confined in an area remote from the cooled area. Finallythere is the realization, that such a long, narrow gap could beconstructed using concentric and relatively rotatable conduits whoselength would tend to reduce heat conduction especially if they are madewith thin walls and low thermal conductivity material, and which couldbe designed with sufficient rigidity to be free from vibration at thespeed of rotation of the machines to be cooled.

The invention features a relatively rotatable cryogenic transferapparatus for transferring fluid between two relatively rotatabledevices which are rotatable relative to each other at significantspeeds. The apparatus includes a housing and a first unit fixed to thehousing and including a first relatively long, stiff, thin, low thermalconductivity conduit. There is a second unit including a secondrelatively long, stiff, thin, low thermal conductivity conduitsurrounding and spaced from the first unit to provide a first relativelylong, narrow relative motion gap that provides a relatively stagnantenvironment in which convection currents are minimized and vapor fromthe fluid acts as an insulator. First means for relatively rotatablyinterconnecting the housing and second unit for maintaining the housingand in uniform spaced alignment is disposed proximate the area where thefirst unit is fixed to the housing so that its heat producing relativemotion contacting parts are remote from the supercooled portion of theapparatus. Second means for relatively rotatably interconnecting thehousing and second unit is disposed in a second ambient temperatureportion of the apparatus spaced from the first ambient temperatureportion and remote from the cooler portions of the apparatus. First portmeans are located in the housing between the first and second ambienttemperature portions. The second unit includes a third relatively long,stiff, thin, low thermal conductivity conduit surrounding the secondconduit. The third conduit is spaced from the housing to provide asecond relatively long, narrow, relative motion gap extending from thefirst port means to the first ambient temperature portion and a thirdrelatively long, narrow relative motion gap extending from the firstport means to the second ambient temperature portion. Each of the secondand third relative motion gaps provides a relatively stagnantenvironment in which convection currents are minimized and vapor fromthe fluid acts as an insulator. There are first sealing means betweenthe housing and the second unit in the first ambient temperature portionfor sealing the ambient temperature end of the first relative motion gapand of the second relative motion gap; and there are second sealingmeans between the housing and second unit in the second ambienttemperature end of the third relative motion gap.

DISCLOSURE OF PREFERRED EMBODIMENT Other objects, features andadvantages will occur from the following description of a preferredembodiment and the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional diagram of the coupling portion ofa cryogenic transfer system.

FIGS. 2a and 2b taken together form a schematic cross-sectional diagramof a preferred embodiment of a cryogenic transfer system according tothis invention with portions of the conduits broken away to showinternal structure.

FIG. 3 is a schematic, diagrammatic, axonometric view of a portion of acryogenic generator which may use the cryogenic transfer system of thisinvention.

There is shown in FIG. 1 a portion of a cryogenic transfer system 8including a stationary section 10 and a rotating section 12. Sections 10and 12 are relatively rotatably interconnected by an alignment bearing14 having an outer race 16 carried by stationary section 10 and an innerrace 18 carried on sleeve 20 mounted on rotating section 12. Two rows ofball bearings 22 and 24 are disposed between inner race 18 and outerrace 16. Transfer of the supercooled fluid, typically liquid Helium, isaccomplished by means of two units relatively rotatable with respect toone another. In FIG. 1 the relative rotation is accomplished by one unitincluding stationary section 10 and another unit including rotatingsection 12. The first unit also includes a Helium inlet/outlet tube 30which is connected at its lower end 32 to a second larger tube 34 whichis coaxial with and spaced about tube 30. The volume between outer tube34 and inner tube 30 constitutes a vacuum conpartment 36 for insulatingthe inner tube 30 that carries the liquid Helium. In FIG. 1 and theother figures of the drawing wherever tubes are shown their walls areindicated by a single, heavy line, even though the view is actually incross-section, in order to clarify the drawings and to eliminateconfusion which might occur when a great number of parallel lines appearclose together in a drawing.

The second unit in addition to section 12 includes a first tube 40concentric with, surrounding and spaced from tube 34 and a second tube42 surrounding, spaced from and concentric with tube 40. The spacebetween tubes 40 and 42 is sealed at the upper end 44 and the lower end,not shown, to form a vacuum compartment 46 which surrounds the liquidHelium as it leaves the lower end of tube 30, arrow 48, and descends intube 40. The space between tubes 40 and 34 is the relative motion gap50.

The upper end of relative motion gap 50 communicates with an annularvolume 52 which contains a graphite seal 54 that bears on the hardenedStellite face of seat ring 56, attached to sleeve 20; graphite seal 54is urged downward in sliding contact with seat ring 56 by means of aspring 58. A second annular seal 60 engages the side of annular, carbonface seal 54 and bears on section 10.

In operation the supercooled fluid e.g. liquid Helium at 4.2K entersthrough the top of tube 30 and descends downwardly to the end of tube 30wherefrom it descends farther within tube 40. At this point thecryogenic fluid has been transferred from the fixed to the moving bodyand may be directed within the moving body to accomplish the cooling asdesired, vapor at approximately 4.2K rising from the supercooled fluidmoves upward through tube 40 and then through the relative motion gap 50to fill space 52 where it encounters seals 54 and 60. Ducts or othervent means are provided in the apparatus to be cooled associated withsection 10 to remove the Helium gas but neither the vents nor theapparatus is shown. A temperature gradient from 4.2K at the lower end ofgap 50 to room temperature at the upper end of gap 50 and in annularvolume 52 occurs in the vapor. Thus the sealing apparatus, i.e. seals 54and 60, since they are located in a room temperature environment remotefrom the supercooled fluid, are prevented from contributing anysubstantial amount of their frictional heat to the supercooled fluid.Similarly, the alignment bearing 14 is also located remote from thesupercooled fluid area at the room temperature end of the system so thatit, too, is prevented from passing any substantial amount of heat to thesupercooled fluid. Significantly, the path of the liquid Helium duringits entire journey through tube 30 and within tube 40 and beyond issurrounded by one or more vacuum compartments. Initially as it movesthrough tube 30 to the portion of tube 30 located within section 10there is provided the vacuum compartment 36. Then slightly below the topsection 12 at end 44, the second vacuum compartment 46 envelops tube 30,34 and tube 40 so that as the liquid Helium leaves the end 32 of tube 30jacketed by vacuum compartment 36 it is still surrounded by vacuumcompartment 46.

In order to minimize heat transfer by centrifugal convection in therelative motion gap 50, a primary source of heat transfer, the relativemotion gap 50 is made as narrow as possible. The heat transfer bycentrifugal convection may be expressed as:

where:

q is the heat transfer rate P, is the prandtl number of helium C,, isthe specific heat at constant pressure of helium p, is the density at 32of helium a, is the viscosity at 32 of helium w is the frequency ofrotation of the rotating parts T is the temperature at 32 r is the meanradius of the relative motion gap 50 h is the width of the relativemotion gap 50 L is the length of tube 34 from section to end 32 and ofrelative motion gap 50 T is the temperature at 52 For the coupling shownin FIG. 1:

C 5.2 Joules/gram Kelvin p 0.0l67 gram/cubic centimeter p. 12.7 X 10gram/centimeter second to 377 radians/second T 4.2 Kelvin r 0. 128inches h 0.0075 inches L 2 inches T 300 Kelvin q 0.07 X 10' watts Thetubes 34 and 40 are at room temperature at end 44 and at 42 K at end 32.Any heat conducted along the metal walls of the tubes adversely affectsthe thermal insulating properties of the apparatus. Tubes are made assmall in thickness and as long as possible consistent with vibrationalrequirements in order to minimize heat conduction along the tubes. Theheat transferred from the warm region 52 to the cold region 32 byconduction is given by:

q FA (AT/l) where q is the heat transfer rate F is the means thermalconductivity between 52 and AT is the difference in temperature between52 and I is the distance between 52 and 32 A is the cross-section-areafor heat conduction between 52 and 32 Th us in FIG. 1:

k 0.25 Watts/inch Kelvin AT 300K I 2 inches A 0.01144 square inch q0.429 watts Vibrational requirements are important because anysubstantial vibration of the tubes 34 and 40 causes them to violate thespace of relative motion gap and disturb the relatively stagnant columnof Helium vapor which acts as an insulator against heat transfer. Inextreme cases tube 34 might be caused to contact tube 40 therebygenerating heat, and causing mechanical interference.

Tubes 30 and 34 can execute lateral vibrations as a cantilevered beam.The lowest frequency for free or natural vibrations of a thin walled,cylindrical, cantilevered beam is:

r 0.046 inch 1 2 inches w 910 l/seconds This is sufficiently higher thanthe typical operating speed of the machine, which is 377 l/seconds thusthe machine frequency is always lower than the lowest vibrationfrequency and a resonant condition is avoided during normal operation.Although all three factors of conduction, vibration and convection aretreated, the apparatus is designed most conservatively for centrifugalconvection.

Preferably, as is the case in FIG. 1, the inner unit in cluding tubes 30and 34 is kept stationary and the outer unit including tubes 40 and 42is rotated but this is not a limitation. However, this arrangement ispreferred because vortices which adversely affect stability in the vaporcolumns may be produced when the inner unit is rotated and the outerunit remains stationary. When the outer unit rotates greater stabilityis possible because centrifugal force generated by the rotation tends tomove the gas towards the surface of tube 40. Relative motion gap 50 ismaintained as small as possible within the limitations of mechanicalalignment in order to minimize centrifugal convection currents in thegap which might adversely affect the insulating temperature gradientcapability of the relatively stagnant vapor column in the gap. Withtubes 30 and 34 having O.D.s of 0.065" and 0.120" and wall thicknessesof 0.009 and 0.013", respectively, and tubes 40 and 42 having O.D.s of0.250 and 0.165" and wall thicknesses of 0.015" and 0.015",respectively, a gap of0.008 inches for relative motion gap is workable.

A preferred embodiment of a relatively rotatable I transfer systemhaving multiple inlet/outlet connections which may be used inconjunction with a closed refrigeration loop or to maintain more thanone stream of supercooled fluid flowing through the system, is shown inFIGS. 2a and 2b. System 70 includes a housing 72 which includes solidportions 74, 76, 78 typically formed in two parts joined together atflanges 74, 76, 78' with bolts and suitable sealing means, not shown,and vacuum jackets.

Jacket 80 is formed of an inner tube 84 surrounded by a concentric,spaced outer tube 86 between which the vaccum compartment 88 is formed.Vacuum jacket 80 also includes an inlet/outlet connection 90 whichcommunicates with the interior of the vacuum jacket 80 and includes atube 92 surrounded by a second tube 94 between which is formed vacuumarea 96, an extension of vacuum compartment 88. Similarly vacuum jacket82 includes an inner cylindrical tube 98 and an outer tube 100surrounding, concentric with, and spaced from the inner tube 98 to forma vacuum compartment 102 therebetween. Vacuum jacket 82 also includes aninlet/outlet connection 104 which communicates with the interior of thevacuum jacket 82 and includes an inner tube 106 and an outer tube 108which is concentric with and spaced from the inner tube 106 betweenwhich is formed vacuum area 110, an extension of vacuum compartment 102.

Within housing 72 is a first tube 112 through which liquid Helium may beintroduced into the system and a second tube 114 concentric with andspaced from tube 112 which is sealingly joined to tube 112 at theirlower ends 116. The space between tubes 112 and 114 functions as avacuum compartment 118 and tube 114 is typically fixed in aperture 120of housing 72. Surrounding tube 114 and spaced therefrom by relativemotion gap 122 is a tube 124 and surrounding and spaced therefrom, tube126; the space between tubes 124 and 126 creates a vacuum compartment128.

Tubes 124 and 126 are sealingly joined together at the upper end ofrotatable section 132 which is fixed to one portion of bearing 134 whilethe other portion of bearing 134 is fixed to the stationary housingsection 74. Annular carbon face seal 136 is kept in sliding contact witha seat ring 138 by springs 140; the seat ring 138 is attached and sealedto section 132. An annular static seal 142 mounted in a groove in seal136 completes the seal between the rotating section 132 and stationarysection 74 of housing 72 so that the volume 144 which communicates withthe relative motion gap 122 is sealed from the volume 146; volume 146 isbetween the seals 136 and 142 and bearing 134 is at room temperature.

There is an inner tube 150 spaced from, surrounding,

and concentric with tubes 124 and 126 and an outer tube 152 surrounding,spaced from and concentric with tube 150; the space between tubes 150and 152 creates a vacuum compartment 154 which is sealed at the upperend where tubes 150 and 152 are joined to tube 126 at junction 156. Alow thermal conductivity support spacer 158 may be used in fluid space153 to maintain more rigid alignment between tube 126 and tube 150; lowthermal conductivity spacers such as spacers 125 may also be used in thevarious vacuum compartments. Tube 126' is effectively a continuation oftube 126 insofar as the cryogenic system is concerned even though,physically, tube 126 is a separate tube interconnected with tube 126 byjunction 156. Ports 157 in junction 156 permit fluid in space 153 toenter annular channel 159 in collar 161 having a port 163 to which tube92 is mounted; annular channel 159 also communicates with relativemotion gap 164.

Rotating section 160 is fastened to outer tube 152 which is fixed toloneportion of alignment bearing 162 the other portion of which is fixed tostationary section 76 of housing 72. The space between outer tube 152and the vacuum jacket 80 and section 76 of housing 72 forms a relativemotion gap 164. Relative motion gap 164 extends around tube 152 fromvolume 166 above junction 156 to volume 168 between tube 152 and vacuumjacket 80. Volume 166 communicates with volume 146 since bearing 134 isnot gas tight. Volume 168 is sealed by annular carbon face seal 170which is held in sliding engagement with a seat ring 172, attached torotating section 160 fixed to outer tube 152, by springs 174 and by anannular static seal 176 mounted in an annular groove in seal 170 andbearing on the inner surface of section 76.

Inner tube 180 and outer tube 188 are surrounding and spaced from tube152 to form space 187 and are spaced from each other to form vacuumcompartment 190 between them. Tubes 180 and 188 may be joined to sealthe upper end of space 190 and may be fixed to tube 152 at junction 192.The space to the right of bearing 203, between outer tube 188, andvacuum jacket 82 and fixed section 78 of housing 72 forms a relativemotion gap 194 which communicates with volume 196 and volume 198 whichis sealed by means of an annular carbon face seal 200 which is held insliding contact with the seat ring 202, attached and sealed to generatorshaft 204 by springs 206 and by means of an annular static seal 208mounted in a groove in seal 200;

generator shaft 204 is fixed to outer tube 188. Ports 193 in junction192 permit fluid in space 187 to enter annular channel 189 in collar 19]having port 195 to which tube 106 is mounted. Annular channel 189 alsocommunicates with relative motion gap 194. A spacer 158 similar tospacer 158 may be used in space 187. The transfer system shown in FIG. 2may be extended to any additional number of sections by adding on unitsin a manner similar to that described.

Typical dimensions for the parts and structure of FIGS. 2a and 2b arelisted as follows: tube 112 has a Vs outer diameter and a wall thicknessof 0.02l vacuum compartment 118 has a width of 0.01625; tube 114 has anouter diameter of 3/16 of an inch and a wall thickness of 0.015" and alength of 3%"; relative motion gap 122 has a width of 0.0125"; tube 124has an outer diameter of 4 of an inch and a wall thickness of 0.020;tube 126 has an outer diameter of l3/ l6 of an inch and a wall thicknessof 0.028; tube 152 has an outer diameter of 13/ l 6 of an inch and awall thickness of 0.028"; relative motion gap 164 has a width of0.01125"; tube 84 has an outer diameter of /3 of an inch and a wallthickness of 0.020"; the distance from bearing 134 to bearing 162 is 13inches; tube 188 has an outer diameter of 1%" and a wall thickness of0.028"; relative motion gap 194 has a width of 0.01125; tube 182 has anouter diameter of 1 9/16 and a wall thickness of 0.020"; tube 98 has anouter diameter of 1 9/16 and a wall thickness of 0.020"; and thedistance from bearing 162 to bearing 203 is 13 inches.

In operation the supercooled fluid, such as liquid Helium, may beintroduced through and recovered from any one of the three inlet/outlettubes 112, 92 and 106. Further, tubes 112, 92 and 106 may be used totransfer more than one fluid into or out of the rotor or the same fluidin separate streams in or out of the rotor. For example. liquid Heliummay be introduced through tube 112; as it descends it clears the end 116of tube 112 and continues downwardly within tube 124 to the area whereit is to be utilized. The liquid Helium in the collection area is atapproximately 4.2K. The vapor at 4.2K rises to fill the various relativemotion gaps in the system to provide various temperature gradients inthe range from 4.2K to room temperature. Thus vapor rising with tube 124rises to the end 116 of tube 112 and then moves upwardly in the relativemotion gap 122 and fills volume 144. Seals 136 and 142 are atapproximately room temperature. Similarly vapor moves upwardly in space153 and is moved out by centrifugal force through a number of ports 157in junction 156 to fill relative motion gap 164 and volumes 166 and 168and to leave the system through tube 92 for recovery.

Similarly vapor rising in space 187 is moved outwardly through ports 193in junction 192 to fill relative motion gap 194 and volumes 196 and 198and enter tube 106 for recovery. Typically, with liquid Helium at 4.2Ksupplied through tube 112, Helium gas at to 200K is recovered fromconnection 104 and Helium vapor at 20K is recovered from connection 92.

In certain areas of the device illustrated in FIGS. 1 and 2a and 2bcompensating bellows may be used to accommodate the shrinkage of theinner tube of the double walled transfer tube when it is subject to thesupercooled temperature at the level of liquid Helium or anothersupercooled fluid. Without such accommodation,

especially in the longer transfer tubes the thermal contraction of theinner tube would stress the smaller tube beyond its yield point. Suchcompensating bellows 250 are shown in FIG. 1. Bellows 250 is formed of anumber of e.g. six stainless steel disks with holes in the center andwhich are welded to adjacent disks at their inner and outer perimeters;the end disks are welded to the corresponding portions of outer tube 34.Thus when liquid Helium at approximately 4.2K is present within tube 30and that tube begins to contract, outer tube 34 which at its upper endproximate volume 52 is at approximately room temperature, will be ableto effectively contract also by means of thecompression of bellows 250.Bellows may be included at various points in system 70 such as, forexample, bellows 250', FIG. 2a, attached to tube 86 and bellows 250",FIG. 2b, attached to tube 100.

The transfer system of this invention as illustrated in FIGS. 1 and 2aand 2b may be used to cool the superconducting field windings in therotor of a superconducting generator 219 as shown in FIG. 3. In FIG. 3transfer system 70 serviced by a refrigeration unit 220 functions tocool the superconducting field winding 222 mounted on rotor 224 which isdriven through drive shaft 226 to rotate within armature winding 228.Transfer system 70 includes an inlet tube 112 surrounded by tube 113, anoutlet 90 including tube 92 surrounded by tube 94, and outlet 104including tube 106 surrounded by tube 108. Tube 188 is fixed to section204 of rotor 224 and tube 188 and other tubes 150 and 152, and 124 and126' are brought into the cooling area 240 within rotor 224 where theyare connected to internal piping which effects the cooling of thesuperconducting winding 222 and the mechanical support portions ateither end of rotor 224. Generator 219 also includes an image shield244, removable from shield 246, end flange 248 and many more parts whichhave been omitted for clarity as generator 219 forms no part of thisinvention but is included only to show one typical application ofthecryogenic transfer device.

In FIGS. 2a and 2b the liquid Helium stream is always surrounded by avacuum insulation space or compartment as the Helium moves through thesystem by virture of the fact that each of the overlapping sectionsincludes in it a vacuum space or compartment. All mechanical rubbing,contact, sealing devices and alignment bearings are positioned at theroom temperature portions of the system so that none of the frictionalheat generated thereby will be dissipated in the supercooled portions ofthe system. All tubes are made of thin wall low conductivity materialand are as long as possible consonant with vibrational considerations.Further the relative motion gaps are as long and narrow as possibleconsonant with mechanical and vibrational considerations. There is thusprovided an extremely efficient and workable transfer system whichprovides great flexibility in controlling the flow of the cryogenicfluid and the temperature gradients maintained thereby.

Other embodiments will occur to those skilled in the art and are withinthe following claims:

What is claimed is:

.1. A relatively rotatable cryogenic transfer apparatus for transferringfluid between two relatively rotatable devices which are rotatablerelative to each other at significant speeds said apparatus comprising:

a housing;

a first unit fixed to said housing and including a first relativelylong, stiff, thin, low thermal conductivity conduit and a secondrelatively long, stiff, thin, low

thermal conductivity conduit spaced from and surrounding said firstconduit to form a vacuum insulating space therebetween;

second unit including a third relatively long, stiff,

thin, low thermal conductivity conduit surrounding and spaced from saidfirst unit to provide a first relatively long, narrow relative motiongap that provides a relatively stagnant environment in which convectioncurrents are minimized and vapor from the fluid acts as an insulator,said second unit further including a fourth relatively long, stiff,thin,

low thermal conductivity conduit surrounding and spaced from said thirdconduit to provide a vacuum insulating space therebetween;

first means for relatively rotatably interconnecting said housing andsaid second unit for maintaining said housing and second unit in uniformspaced alignment and having its heat-producing relative motioncontacting parts disposed in a first ambient temperature portion of saidapparatus proximate the area where said first unit is fixed to saidhousing remote from the supercooled portions of the apparatus, includingan alignment bearing with two relatively rotatable parts one fastened tosaid housing the other to said second unit;

second means for relatively rotatably interconnecting said housing andsaid second unit disposed in a second ambient temperature portion ofsaid apparatus spaced from said first ambient temperature portion andremote from the cooler portions of said apparatus, including analignment bearing with two relatively rotatable parts one fastened tosaid housing the other to said second unit;

first port means in said housing between said first and second ambienttemperature portions;

said fourth conduit being spaced from'said housing to provide a secondrelatively long, narrow, relative motion gap extending from said firstport means to said first ambient temperature portion and a thirdrelatively long, narrow, relative motion gap extending from said firstport means to said second ambient temperature portion. each of saidsecond and third relative motion gaps providing a relatively stagnantenvironment in which convection currents are minimized and vapor fromthe fluid acts as an insulator;

first sealing means between said housing and second unit in said firstambient temperature portion for sealing the ambient temperature end ofsaid first relative motion gap and of said second relative motion gapincluding a first sliding seal engaging one of said housing and saidsecond unit and a second seal engaging the first seal and the other ofsaid housing and said second unit; and

second sealing means between said housing and said second unit in saidsecond ambient temperature portion for sealing the ambient temperatureend of said third relative motion gap, including a first sliding sealengaging one of said housing and said second unit and a second sealengaging the first seal and the other of said housing and said secondunit.

2. The apparatus of claim 1 further including a third unit fixed to saidsecond unit and including a fifth relatively long, stiff, thin, lowthermal conductivity conduit surrounding and spaced from said fourthconduit and forming a vacuum insulated space therebetween;

third means for relatively rotatably interconnecting said housing andsaid third unit in a third ambient temperature portion of said apparatusspaced from said second ambient temperature portion and fan ther spacedfrom said first ambient temperature portion and remote from the coolerportions of said apparatus, including an alignment bearing with tworelatively rotatable parts one fastened to said housing the other tosaid third unit;

second port means in said housing between said second and third ambienttemperature portions;

said fifth conduit being spaced from said housing to provide a fourthrelatively, long, narrow, relative motion gap extending from said secondport means to said second ambient temperature portion and a fifthrelatively long, narrow, relative motion gap extending from said secondport means to said third ambient temperature portion, each of saidfourth and fifth relative motion gaps providing a relatively stagnantenvironment in which convection currents are minimized and vapor fromthe fluid acts as an insulator;

third sealing means between said housing and third unit in said thirdambient temperature portion for sealing the ambient end of said fifthrelative motion gap, the ambient temperature end of said fourth relativemotion gap being sealed by said second sealing means, including a firstsliding seal engaging one of said housing and said third unit and asecond seal engaging the first seal and the other of said housing andsaid third unit.

3. The apparatus of claim 1 further including third port means in saidfourth conduit and cooperating with said first port means in saidhousing, and a first chamber between said third and fourth conduitsextending from the supercooled portions of said apparatus to said thirdport means, for transporting fluid from the supercooled portion to saidsecond and third relative motion gaps and said first port means.

4. The apparatus of claim 1 further including fourth port means in saidfifth conduit cooperating with said second port means in said housing,and a second chamber between said fifth and fourth conduits extendingfrom the supercooled portion of said apparatus to said cooled portion tosaid fourth and fifth relative motion gaps and said second port means.

1. A relatively rotatable cryogenic transfer apparatus for transferringfluid between two relatively rotatable devices which are rotatablerelative to each other at significant speeds said apparatus comprising:a housing; a first unit fixed to said housing and including a firstrelatively long, stiff, thin, low thermal conductivity conduit and asecond relatively long, stiff, thin, low thermal conductivity conduitspaced from and surrounding said first conduit to form a vacuuminsulating space therebetween; a second unit including a thirdrelatively long, stiff, thin, low thermal conductivity conduitsurrounding and spaced from said first unit to provide a firstrelatively long, narrow relative motion gap that provides a relativelystagnant environment in which convection currents are minimized andvapor from the fluid acts as an insulator, said second unit furtherincluding a fourth relatively long, stiff, thin, low thermalconductivity conduit surrounding and spaced from said third conduit toprovide a vacuum insulating space therebetween; first means forrelatively rotatably interconnecting said housing and said second unitfor maintaining said housing and second unit in uniform spaced alignmentand having its heatproducing relative motion contacting parts disposedin a first ambient temperature portion of said apparatus proximate thearea where said first unit is fixed to said housing remote from thesupercooled portions of the apparatus, including an alignment bearingwith two relatively rotatable parts one fastened to said housing theother to said second unit; second means for relatively rotatablyinterconnecting said housing and said second unit disposed in a secondambient temperature portion of said apparatus spaced from said firstambient temperature portion and remote from the cooler portions of saidapparatus, including an alignment bearing with two relatively rotatableparts one fastened to said housing the other to said second unit; firstport means in said housing between said first and second ambienttemperature portions; said fourth conduit being spaced from said housingto provide a second relatively long, narrow, relative motion gapextending from said first port means to said first ambient temperatureportion and a third relatively long, narrow, relative motion gapextending from said first port means to said second ambient temperatureportion, each of said second and third relative motion gaps providing arelatively stagnant environment in wHich convection currents areminimized and vapor from the fluid acts as an insulator; first sealingmeans between said housing and second unit in said first ambienttemperature portion for sealing the ambient temperature end of saidfirst relative motion gap and of said second relative motion gapincluding a first sliding seal engaging one of said housing and saidsecond unit and a second seal engaging the first seal and the other ofsaid housing and said second unit; and second sealing means between saidhousing and said second unit in said second ambient temperature portionfor sealing the ambient temperature end of said third relative motiongap, including a first sliding seal engaging one of said housing andsaid second unit and a second seal engaging the first seal and the otherof said housing and said second unit.
 2. The apparatus of claim 1further including a third unit fixed to said second unit and including afifth relatively long, stiff, thin, low thermal conductivity conduitsurrounding and spaced from said fourth conduit and forming a vacuuminsulated space therebetween; third means for relatively rotatablyinterconnecting said housing and said third unit in a third ambienttemperature portion of said apparatus spaced from said second ambienttemperature portion and farther spaced from said first ambienttemperature portion and remote from the cooler portions of saidapparatus, including an alignment bearing with two relatively rotatableparts one fastened to said housing the other to said third unit; secondport means in said housing between said second and third ambienttemperature portions; said fifth conduit being spaced from said housingto provide a fourth relatively, long, narrow, relative motion gapextending from said second port means to said second ambient temperatureportion and a fifth relatively long, narrow, relative motion gapextending from said second port means to said third ambient temperatureportion, each of said fourth and fifth relative motion gaps providing arelatively stagnant environment in which convection currents areminimized and vapor from the fluid acts as an insulator; third sealingmeans between said housing and third unit in said third ambienttemperature portion for sealing the ambient end of said fifth relativemotion gap, the ambient temperature end of said fourth relative motiongap being sealed by said second sealing means, including a first slidingseal engaging one of said housing and said third unit and a second sealengaging the first seal and the other of said housing and said thirdunit.
 3. The apparatus of claim 1 further including third port means insaid fourth conduit and cooperating with said first port means in saidhousing, and a first chamber between said third and fourth conduitsextending from the supercooled portions of said apparatus to said thirdport means, for transporting fluid from the supercooled portion to saidsecond and third relative motion gaps and said first port means.
 4. Theapparatus of claim 1 further including fourth port means in said fifthconduit cooperating with said second port means in said housing, and asecond chamber between said fifth and fourth conduits extending from thesupercooled portion of said apparatus to said fourth port means fortransporting fluid from the supercooled portion to said fourth and fifthrelative motion gaps and said second port means.